1. Field of the Invention
The invention relates to a production method for a color filter which uses a dry etching process.
2. Description of the Related Art
As a method of a color filter for preparing liquid crystal display elements or solid state image pick-up elements, a staining method, a printing method, an electrodeposition method and a pigment dispersion process are known.
The pigment dispersion process is a method of using a radiation sensitive colored composition in which a pigment is dispersed in various photosensitive compositions and producing a color filter by photolithographic method. Since pigments are used in the method, the filter is stable to light, heat, or the like. Further, since patterning in this method is conducted by photolithographic method, registering accuracy is also sufficient and it is considered that the method is suitable for producing color filters for use in large screen color displays or high-definition color displays. Therefore, the method is generally used.
In the case of producing a color filter by the pigment dispersion process, a radiation sensitive composition is coated on a glass support by using a spin coater, a roll coater or the like and drying to form a coating film. Then, colored pixels are obtained by pattern-exposing and developing the coated film. The color filter can be prepared by repeating this process a number of times corresponding to the desired number of color hues.
As the pigment dispersion process, a negative working photosensitive composition in which a photopolymerizable monomer and a photopolymerization initiator are combined with alkali soluble resin is disclosed (e.g., see Japanese Patent Application Laid-Open (JP-A) Nos. 2-181704, 2-199403, 5-273411).
Recently, a further high-definition has been desired for color filters for use in solid image pick-up elements. However, conventional pigment dispersion systems have difficulties in further improving the definition. Further, Because of problems such as generation of color irregularities due to coarse particles of the pigment, a further improvement in the definition is very difficult.
In view of these problems, a technology that uses a dye in place of the pigment has been proposed (e.g., see Japanese Patent Application Laid-Open (JP-A) Nos. 6-75375). However, a curable composition that uses a dye has a problem in that various properties such as light-fastness, thermal resistance, solubility and coating uniformity are generally inferior to that of the pigment. Further, when it is used to prepare a color filter for solid-state imaging elements, since a film thickness of 1.5 μm or less is necessary, a large quantity of a dye has to be added to a curable composition. Accordingly, there is a problem that pattern formability especially deteriorate. For example, the adhesiveness with a substrate and the curability become insufficient and a dye in an exposed area that forms a filter comes off.
Furthermore, irrespective of a pigment or dye as a colorant, when the photolithography process is used to prepare a color filter, components other than the colorant, that is, a binder resin, a photopolymerizable compound and a photopolymerization initiator have to be used much. Accordingly, there is a problem in that a film thickness cannot be thinned.
Recently, from the viewpoint of an improvement of image quality due to reduction of the shading, a further thinner color filter is in demand. Furthermore, owing to the miniaturization of a light-receiving element and a display element, a finer pattern is demanded to form in rectangle. For example, in a liquid crystal display element and a solid-state image pick-up element, the downsizing of a pixel size is forwarded. Accordingly, the color filter also needed to miniaturize. In particular, the miniaturization of the solid-state image pick-up element is remarkable, the solid-state image pick-up element requires a high definition technology that enables to obtain a size of 2.0 μm or less. That is, the existing photolithography process is approaching the limit of the resolving power.
In comparison with a production method for a color filter in which the photolithography process is used, as a process effective for forming a thinner and finer pattern, a dry etching process has been known. The dry etching process has been used as a process of forming a pattern to an evaporated thin film of a colorant (e.g., see Japanese Patent Application Laid-Open (JP-A) Nos. 55-146406). In the dry etching process, when a thin film is formed, in comparison with the photolithography system, while maintaining the spectral characteristics in the same range, a thin film having a film thickness of one half or less of a film thickness formed by the photolithography process can be formed. Furthermore, a pattern formation process in which the photolithography process and the dry etching process are combined is proposed (e.g., see Japanese Patent Application Laid-Open (JP-A) Nos. 2001-249218).